Efficient signaling over access channel

ABSTRACT

An apparatus and method for transmitting an indicator of channel quality while minimizing the use of a broadcast channel is described. A metric of forward link geometry of observed transmission signals is determined. An indicator of channel quality value is determined as a function of the observed transmission signals. An access sequence is selected, randomly, from one group of a plurality of groups of access sequences, wherein each of the plurality of groups of access sequences correspond to different ranges of channel quality values.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/499,705 entitled “EFFICIENT SIGNALING OVER ACCESS CHANNEL” filed Apr.27, 2017, allowed, which is a continuation of U.S. Pat. No. 10,194,463entitled “EFFICIENT SIGNALING OVER ACCESS CHANNEL” filed Aug. 7, 2015,and issued on Jan. 29, 2019, which is a divisional application of U.S.Pat. No. 9,137,822 entitled “EFFICIENT SIGNALING OVER ACCESS CHANNEL”filed Dec. 22, 2004, and issued on Sep. 15, 2015, which claims priorityto Provisional Application No. 60/590,113, entitled “EFFICIENT CQISIGNALING OVER ACCESS CHANNEL,” filed Jul. 21, 2004, and assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND Field

The invention relates generally to wireless communications, and morespecifically to data transmission in a multiple access wirelesscommunication system.

Background

An access channel is used on the reverse link by an access terminal forinitial contact with an access point. The access terminal may initiatean access attempt in order to request dedicated channels, to register,or to perform a handoff, etc. Before initiating an access attempt, theaccess terminal receives information from the downlink channel in orderto determine the strongest signal strength from nearby access points andacquire downlink timing. The access terminal is then able to decode theinformation transmitted by the given access point on a broadcast channelregarding choice of parameters governing the access terminal's accessattempt.

In some wireless communication systems, an access channel refers both toa probe and message being rendered. In other wireless communicationsystems, the access channel refers to the probe only. Once the probe isacknowledged, a message governing the access terminal's access attemptis transmitted.

In an orthogonal frequency division multiple access (OFDMA) system, anaccess terminal typically separates the access transmission to betransmitted on the access channel into parts, a preamble transmissionand a payload transmission. To prevent intra-cell interference due tolack of fine timing on the reverse link during the access preambletransmission, a CDM-based preamble transmission may betime-division-multiplexed with the rest of the transmissions (i.e.,traffic, control, and access payload). To access the system, the accessterminal then randomly selects one PN sequence out of a group of PNsequences and sends it as its preamble during the access slot.

The access point searches for any preambles (i.e., all possible PNsequences) that may have been transmitted during the access slot. Accesspreamble transmission performance is measured in terms of collisionprobability, misdetection probability and false alarm probability.Collision probability refers to the probability that a particularpseudo-random (PN) sequence is chosen by more than one access terminalas its preamble in the same access slot. This probability is inverselyproportional to the number of preamble sequences available. Misdetectionprobability refers to the probability that a transmitted PN sequence isnot detected by the base station. False alarm probability refers to theprobability that an access point erroneously declared that a preamblehas been transmitted while no preamble is actually transmitted. Thisprobability increases with the number of preambles available.

The access point then transmits an acknowledgment for each of thepreambles detected. The acknowledgement message may include a PNsequence detected, timing offset correction, and index of the channelfor access payload transmission. Access terminals whose PN sequence isacknowledged can then transmit the respective access payload using theassigned resource.

Because the access point has no prior knowledge of where the accessterminal is in the system (i.e. what its power requirements, bufferlevel, or quality of service may be), the acknowledgement message isbroadcasted at a power level high enough such that all access terminalsin the given cell can decode the message. The broadcast acknowledgementis inefficient as it requires a disproportionate amount of transmitpower and/or frequency bandwidth to close the link. Thus, there is aneed to more efficiently send an acknowledgment message to accessterminals in a given cell.

SUMMARY

Embodiments of the invention minimize use of a broadcast acknowledgementchannel during its preamble transmission. Embodiments of the inventionfurther addresses how information regarding forward link channel qualitycan be efficiently signaled over the access channel during accesspreamble transmission.

In one embodiment, an apparatus and method for transmitting an indicatorof channel quality minimizing the use of a broadcast channel isdescribed. A metric of forward link geometry of observed transmissionsignals is determined. An indicator of channel quality value isdetermined as a function of the observed transmission signals. An accesssequence is selected, randomly, from one group of a plurality of groupsof access sequences, wherein each of the plurality of groups of accesssequences correspond to different ranges of channel quality values.

The metric of forward link geometry may be determined as a function ofobserved pilot signals, noise, and/or traffic on data channels. Thequantity of access sequences in the plurality of groups access sequencesare distributed non-uniformly. In an embodiment, the access sequencesare distributed to reflect the distribution of access terminals aboutthe access point. In another embodiment, the access sequences aredistributed in proportion to the number of access terminals that need agiven amount of power needed to send an indicator of acknowledgment tothe access terminal.

In another embodiment, a method of partitioning a plurality of accesssequences, is described. A probability distribution of a plurality ofaccess terminals about an access point is determined. The probabilitydistribution is determined as a function of a plurality of accessterminals having CQI values within a predetermined ranges. Groups ofaccess sequences are assigned in proportion to the probabilitydistribution. Access sequences can be reassigned as a function of achange in distribution of access terminals about the access point.

In yet another embodiment, an apparatus and method of transmitting anacknowledgement of a detected access sequence is described. An accesssequence is received. The access sequence can be looked-up in a look-uptable, stored in memory, to determine at least one attribute of thegiven access terminal (as a function of the access sequence). Theattribute can be information such as a channel quality indicator, abuffer level and a quality of service indicator. Information is thentransmitted to the access terminal, where the information iscommensurate and consistent with the attribute. Information transmittedmay include an indicator of acknowledgment. The indicator ofacknowledgment may be transmitted over a shared signaling channel(SSCH).

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 illustrates a block diagram of a transmitter and a receiver;

FIG. 2 illustrates the access probe structure and the access probesequence;

FIG. 3 illustrates a traditional call flow between an access terminaland an access point;

FIG. 4 illustrates an embodiment of the invention that avoids the use ofthe broadcast acknowledgement;

FIG. 5 illustrates a cell partitioned using uniform spacing;

FIG. 6 illustrates a diagram showing weighted partitioning based onquantized CQI values;

FIG. 7 illustrates a table stored in memory that partitions the group ofaccess sequences into sub-groups of access sequences based on a varietyof factors; and

FIG. 8 illustrates a process for dynamically allocating accesssequences.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

The techniques described herein for using multiple modulation schemesfor a single packet may be used for various communication systems suchas an Orthogonal Frequency Division Multiple Access (OFDMA) system, aCode Division Multiple Access (CDMA) system, a Time Division MultipleAccess (TDMA) system, a Frequency Division Multiple Access (FDMA)system, an orthogonal frequency division multiplexing (OFDM)-basedsystem, a single-input single-output (SISO) system, a multiple-inputmultiple-output (MIMO) system, and so on. These techniques may be usedfor systems that utilize incremental redundancy (IR) and systems that donot utilize IR (e.g., systems that simply repeats data).

Embodiments of the invention avoid use of a broadcast acknowledgementchannel by having the access terminals indicate a parameter, such asforward link channel quality (i.e., CQI), buffer level requirements,quality of service requirements, etc., during its preamble transmission.By having the access terminals indicate forward link channel quality,the access point can transmit each acknowledgment on a channel using anappropriate amount of power for a given access terminal or group ofaccess terminals. In the case of the acknowledgment message beingtransmitted to a group of access terminals, an acknowledgment message issent to multiple access terminals who have indicated the same or similarCQI values (within a range). Embodiments of the invention furtheraddress how CQI can be efficiently signaled over the access channelduring access preamble transmission.

An “access terminal” refers to a device providing voice and/or dataconnectivity to a user. An access terminal may be connected to acomputing device such as a laptop computer or desktop computer, or itmay be a self contained device such as a personal digital assistant. Anaccess terminal can also be called a subscriber station, subscriberunit, mobile station, wireless device, mobile, remote station, remoteterminal, user terminal, user agent, or user equipment. A subscriberstation may be a cellular telephone, PCS telephone, a cordlesstelephone, a Session Initiation Protocol (SIP) phone, a wireless localloop (WLL) station, a personal digital assistant (PDA), a handhelddevice having wireless connection capability, or other processing deviceconnected to a wireless modem.

An “access point” refers to a device in an access network thatcommunicates over the air-interface, through one or more sectors, withthe access terminals or other access points. The access point acts as arouter between the access terminal and the rest of the access network,which may include an IP network, by converting received air-interfaceframes to IP packets. Access points also coordinate the management ofattributes for the air interface. An access point may be a base station,sectors of a base station, and/or a combination of a base transceiverstation (BTS) and a base station controller (BSC).

FIG. 1 illustrates a block diagram of a transmitter 110 and a receiver150 in a wireless communication system 100. At transmitter 110, a TXdata processor 120 receives data packets from a data source 112. TX dataprocessor 120 processes (e.g., formats, encodes, partitions,interleaves, and modulates) each data packet in accordance with a modeselected for that packet and generates up to T blocks of data symbolsfor the packet. The selected mode for each data packet may indicate (1)the packet size (i.e., the number of information bits for the packet)and (2) the particular combination of code rate and modulation scheme touse for each data symbol block of that packet. A controller 130 providesvarious controls to data source 112 and TX data processor 120 for eachdata packet based on the selected mode. TX data processor 120 provides astream of data symbol blocks (e.g., one block for each frame), where theblocks for each packet may be interlaced with the blocks for one or moreother packets.

A transmitter unit (TMTR) 122 receives the stream of data symbol blocksfrom TX data processor 120 and generates a modulated signal. Transmitterunit 122 multiplexes in pilot symbols with the data symbols (e.g., usingtime, frequency, and/or code division multiplexing) and obtains a streamof transmit symbols. Each transmit symbol may be a data symbol, a pilotsymbol, or a null symbol having a signal value of zero. Transmitter unit122 may perform OFDM modulation if OFDM is used by the system.Transmitter unit 122 generates a stream of time-domain samples andfurther conditions (e.g., converts to analog, frequency upconverts,filters, and amplifies) the sample stream to generate the modulatedsignal. The modulated signal is then transmitted from an antenna 124 andvia a communication channel to receiver 150.

At receiver 150, the transmitted signal is received by an antenna 152,and the received signal is provided to a receiver unit (RCVR) 154.Receiver unit 154 conditions, digitizes, and pre-processes (e.g., OFDMdemodulates) the received signal to obtain received data symbols andreceived pilot symbols. Receiver unit 154 provides the received datasymbols to a detector 156 and the received pilot symbols to a channelestimator 158. Channel estimator 158 processes the received pilotsymbols and provides channel estimates (e.g., channel gain estimates andSINR estimates) for the communication channel. Detector 156 performsdetection on the received data symbols with the channel estimates andprovides detected data symbols to an RX data processor 160. The detecteddata symbols may be represented by log-likelihood ratios (LLRs) for thecode bits used to form the data symbols (as described below) or by otherrepresentations. Whenever a new block of detected data symbols isobtained for a given data packet, RX data processor 160 processes (e.g.,deinterleaves and decodes) all detected data symbols obtained for thatpacket and provides a decoded packet to a data sink 162. RX dataprocessor 160 also checks the decoded packet and provides the packetstatus, which indicates whether the packet is decoded correctly or inerror.

A controller 170 receives the channel estimates from channel estimator158 and the packet status from RX data processor 160. Controller 170selects a mode for the next data packet to be transmitted to receiver150 based on the channel estimates. Controller 170 also assemblesfeedback information. The feedback information is processed by a TX dataprocessor 182, further conditioned by a transmitter unit 184, andtransmitted via antenna 152 to transmitter 110.

At transmitter 110, the transmitted signal from receiver 150 is receivedby antenna 124, conditioned by a receiver unit 142, and furtherprocessed by an RX data processor 144 to recover the feedbackinformation sent by receiver 150. Controller 130 obtains the receivedfeedback information, uses the ACK/NAK to control the IR transmission ofthe packet being sent to receiver 150, and uses the selected mode toprocess the next data packet to send to receiver 150. Controllers 130and 170 direct the operation at transmitter 110 and receiver 150,respectively. Memory units 132 and 172 provide storage for program codesand data used by controllers 130 and 170, respectively.

FIG. 2 illustrates the access probe structure and the access probesequence 200. In FIG. 2, Ns probe sequences are shown, where each probesequence has Np probes. The media access control layer (MAC) protocoltransmits access probes by instructing the physical layer to transmit aprobe. With the instruction, the access channel MAC protocol providesthe physical layer with a number of elements, including, but not limitedto, the power level, access sequence identification, pilot PN of thesector to which the access probe is to be transmitted, a timing offsetfield and a control segment field. Each probe in a sequence istransmitted at increasing power until the access terminal receives anaccess grant. Transmission is aborted if the protocol received adeactivate command, or if a maximum number of probes per sequence havebeen transmitted. Prior to transmission of the first probe of all probesequences, the access terminal forms a persistence test which is used tocontrol congestion on the access channel.

FIG. 3 illustrates a traditional call flow between an access terminaland an access point 300. Access terminal 304 randomly selects apreamble, or PN sequence, out of a group of PN sequences and sends 308the preamble during the access slot to the access point 312. Uponreceipt, the access point 312 then transmits 316 an access grant,including a broadcast acknowledgement, for each of the preamblesdetected. This acknowledgement is a broadcasted acknowledgementtransmitted at a high enough power such that all of the access terminalsin a given cell are able to decode the broadcast acknowledgement. Thisis deemed necessary because the access point has no prior knowledgewhere the access terminals are in the system, and thus has no knowledgeas to the power level necessary for the access terminal to decode thebroadcasted acknowledgement. On receipt of the accent grant 316, accessterminal 304 sends 320 the payload as per the defined resourcesallocated in the access grant.

The broadcast acknowledgement transmission described above is relativelyinefficient as it requires a disproportionate amount of transmit powerand/or frequency bandwidth to close the link. FIG. 4 illustrates anembodiment 400 that avoids the use of the broadcast acknowledgement. Anaccess terminal observes 408 transmissions from access points. Inobserving, the access terminal determines the power of transmissions itreceives. These observations typically involve determining forward linkchannel quality from observed acquisition pilot signal transmissions orpilot transmissions as part of a shared signaling channel (SSCH)channel.

The access terminal 404 then randomly selects a preamble, or accesssequence, out of a group of access sequences and sends the preamble 410to the access point 412. This preamble is transmitted along with someknowledge of forward link channel quality (CQI). CQI information may betransmitted as within the preamble, or appended to it. In anotherembodiment, an access sequence is randomly chosen out of a plurality ofgroups of access sequences, where each group of access sequences isdesignated for a range of CQI values. For example, indications offorward link channel quality may be observed pilot signal power. Theobserved pilot signal power may be quantized to CQI values based on apredetermined set of values. Thus, a given range of received pilotsignal power may correspond to a given CQI value. Accordingly, theaccess point 412 may determine the CQI of a given access terminal byvirtue of the access sequence chosen by the access terminal.

Because the access terminal sends an indicator of forward link channelquality during its initial access attempt with the access point 412, theaccess point 412 has the knowledge needed to transmit 416 eachacknowledgement on a channel using an appropriate amount of power forthe designated access terminal 404. In an embodiment, the acknowledgmentmessage may be sent to a group of access terminals having the same orsimilar CQI values. This may be through use of the SSCH. Thus, based onthe power level needed for the access terminal to successfully receivethe transmission, the access point sends the acknowledgement message inthe appropriate section of the SSCH message.

In addition to CQI information, the access terminal may send otherinformation of interest to the access point during the initial accessphase. For example, the access terminal may send a buffer levelindicator, indicating the amount of data the access terminal intends tosend to the access point. With such knowledge, the access point is ableto appropriately dimension initial resource assignments.

The access terminal may also send information regarding priority groupsor quality of service. This information may be used to prioritize accessterminals in the event of limited access point capability or systemoverload.

Upon receipt of the access grant message by the access terminal, theaccess terminal 404 sends 420 payload as per the resources defined inthe access grant message. By receiving additional information during theinitial access phase, the access point will be able to take advantage ofknowing the CQI, buffer level and quality of service information as partof the access grant message.

FIG. 5 illustrates a cell 500 partitioned using uniform spacing. Thecell is divided into a number of regions R, wherein each region isdefined by having a probability of observed metrics within a givenrange. In an embodiment, observations of forward link geometry are used.For example, metrics such as C/I, where C is the received pilot powerand I is the observed noise, may be used. Also, C/(C+I) may be used. Inother words, some measure that utilizes observed signal power and noiseis used. These observed metrics correspond to given CQI values, or valueranges, which thus define the region. For example, Region R₁ defines aRegion having CQI values corresponding to power and/or noise levelsgreater than P₁. Region R₂ defines a region having CQI valuescorresponding to power and/or noise levels such that P₂>R₂>P₁.Similarly, Region R₃ defines a Region having CQI values corresponding topower and/or noise levels such that P₃>R₃>P₂, and so on. Region R_(N-1)has CQI values corresponding to power and/or noise levels such that theyfall in the range of P_(x)>R_(N-1)>P_(y). Similarly, Region R_(N) hasCQI values corresponding to power and/or noise levels observed <P_(x).

Theoretically, by choosing to transmit one of N possible preamblesequences, up to log 2(N) bits of information may be conveyed. Forexample, when N=1024, as many as log 2(1024)=10 bits may be conveyed.Thus, by choosing which preamble sequence to transmit, it is possiblefor user dependent information to be embedded as part of the preambletransmission.

A commonly used technique is to partition then N preamble sequences intoM distinct sets, labeled {1,2, . . . , M} To signal one of log₂(M)possibilities (i.e., log₂(M) bits), a sequence in an appropriate set ischosen and transmitted. For instance, to signal message index k€{1,2, .. . , M}, a sequence in the k^(th) set is (randomly) chosen andtransmitted. Assuming correct detection at the receiver, the transmittedinformation (i.e., the log₂(M)-bit message) can be obtained based on theindex of the set that the received sequence belongs to.

In a uniform partitioning strategy, where the N preamble sequences areuniformly partitioned into M groups (i.e., each group contains N/Msequences). Based on the measured CQI value, one of the preamblesequences from an appropriate set is selected and transmitted. Thecollision probability, then, depends on the mapping/quantization of themeasured CQI and the number of simultaneous access attempts.

This can be illustrated by considering a simple 2-level quantization ofCQI (i.e., M=2), with Pr(M(CQI)=1)=α and Pr(M(CQI)=1)=α, where M(x) is aquantization function mapping the measured CQI value into one of the twolevels.

With uniform access sequence partitioning, the N preamble sequences arepartitioned into two sets with N/2 sequences in each set. As by example,assume that there are two simultaneous access attempts (i.e., exactlytwo access terminals are trying to access the system in each accessslot). The collision probability is given by

${\alpha^{2}\frac{1}{( \frac{N}{2} )}} + {( {1 - \alpha} )^{2}{\frac{1}{( \frac{N}{2} )}.}}$

With probability α², the two access terminals wish to send M=1 (i.e.,they both have quantized CQI level=1). Since there are N/2 preamblesequences to choose from in the first set, the collision probability(given that both access terminals choose their sequence from this set)is 1/(N/2). Following the same logic, the collision probability for theother set can be derived.

Thus, the overall collision probability depends on the parameter a andnumber of simultaneous access attempts. The collision probability can beas high as 2/N (α=0,1) or as low as 1/N (α=0.5). Thus, the best choiceof α in this case is α=0.5. However, it is unclear whether the CQIquantization function that results in α=0.5 is a desirable function.

The access point will transmit the acknowledgment channel at the powerlevel required to close the link as indicated by the CQI level. In thisexample, with probability α, the access point has to transmit at thepower corresponding to that of a broadcast channel and with probability1-α, the access point can transmit at some lower power. Thus, withα=0.5, half the time the access point has to broadcast theacknowledgment channel. On the other hand, by choosing α=0.5, the accesspoint is forced to broadcast the acknowledgement channel less frequentlybut incurring an increase in the transmit power in the remaining of thetime and higher overall collision probability.

FIG. 6 illustrates a diagram showing weighted partitioning 600 based onquantized CQI values. The region is partitioned into various regionsthat are not of a uniform space, but are rather partitioned based onquantized CQI values that are weighted. By weighting the regions,additional preamble sequences are available in regions that have ahigher probability of access terminals being in that region (i.e., ahigher mass function). For example, regions 604, 608, and 612 are largerregions that may correspond to having a larger number of accesssequences available. Conversely, regions 616 and 620 are smaller regionsthat may indicate smaller quantities of users present and thus feweraccess sequences available. Thus, the regions may be partitioned havingsome prior knowledge as to the distribution of C/I or received power ina specified range in a given cell. It is contemplated that geographicregions may not always represent concentrations of users within givenCQI ranges. Rather, the graphical representations of non-uniform spacingis to indicate the non-uniform distribution of access sequences througha given cell region.

In an embodiment, the probability distribution of access terminalswithin the cell may be dynamic based on the distribution of accessterminals over time. Accordingly, certain partitioned regions may belarger or smaller based on the absence or presence of access terminalsat a given time of the day, or otherwise adjusted as a function of theconcentration of access terminals present in a given CQI region.

Thus, the sequences available for initial access are divided into Nnumber of partitions. The access terminal determines the partition to beused for the access attempt based on at least the observed pilot powerand buffer level. It is contemplated that the partition may also bedetermined on a number of other factors, such as packet size, traffictype, bandwidth request, or quality of service. Once the partition isdetermined, the access terminals select the sequence ID using a uniformprobability over that partition. Of the available sequences for access,a subset of sequences is reserved for active set operations, and anothersubset of sequences are available for initial access. In one embodiment,sequences 0, 1 and 2 are reserved for active set operations, andsequences 3 through the total number of access sequences are availablefor initial access.

The size of each partition is determined by the access sequencepartition field in the system information block. This is typically partof the sector parameter. A particular partition number N comprisessequence identifiers ranging from a lower threshold, partition N lower,to an upper threshold, partition N upper. Both thresholds are determinedusing the partitions size, partially provided in table 1 below:

Access Sequence Partition N Size (N from 1 to 8) Partition 1 2 3 4 5 6 78 00000 0 0 0 0 0 0 0 0 00001 S2 S2 S2 S2 S2 S2 S2 S2 00010 S3 S3 S S1S1 S1 S1 S1 00011 S1 S1 S1 S3 S3 S3 S1 S1 00100 S1 S1 S1 S1 S1 S1 S3 S300101 S3 S1 S1 S3 S1 S1 S3 S1 00101 S1 S3 S1 S1 S3 S1 S1 S3 00110 S1 S1S3 S1 S1 S3 S1 S1 00111 S3 S3 S1 S3 S1 S1 S1 S1 01000 S1 S1 S1 S3 S3 S1S3 S1

Thus, in this embodiment the access terminal selects its pilot levelbased on the ratio, measured in decibels, of the acquisition pilot powerfrom the sector where the access attempt is being made to the totalpower received in the acquisition channel time slot. The pilot thresholdvalues are determined based on the pilot strength segmentation field ofthe system information message.

Embodiments describe a technique whereby the access sequence space ispartitioned according to the statistics of the quantized CQI. Moreprecisely,

P=[p ₁ p ₂ . . . p _(M)]

is the probability mass function of the quantized CQI values, where

Pr(CQI=1)=p ₁ , Pr(CQI=2)=p ₂ , . . . , Pr(CQI=M)=p _(M)).

The access sequence space is then partitioned to have a similarprobability mass function. That is, the ratio of the number of accesssequences in each set to the total number of access sequences should beproportional, such that

$p = {\lbrack {p_{1}\mspace{14mu} p_{2}\mspace{14mu} \ldots \mspace{14mu} p_{M}} \rbrack \mspace{14mu} ( {{i.e.},{( {\frac{N_{1}}{N},\frac{N_{2}}{N},\ldots \mspace{11mu},\frac{N_{M}}{N}} ) = ( {p_{1}\mspace{14mu} p_{2}\mspace{14mu} \ldots \mspace{14mu} p_{M}} )},} }$

where N_(k) is the number of access sequences in set K€{1,2, . . . , M}

In the example describing the 2-level CQI quantization function yieldsthe following:

Pr(M(CQI)=1)=α and Pr(M(CQI)=2)=1−α

The number of access sequences in each set is, therefore, (α)N and(1−α)N, respectively. The resulting collision probability is

${{{\alpha^{2}\frac{1}{( {\alpha \; N} )}} + {( {1 - \alpha} )^{2}\frac{1}{( {( {1 - \alpha} )\; N} )}}} = {{\frac{\alpha}{N} + \frac{( {1 - \alpha} )}{N}} = \frac{1}{N}}},$

which is the smallest collision probability possible.

For a more general setting with M possible CQI levels and U simultaneousattempts, the analytical expression of the collision probability becomesmore complex.

In another example, consider M=6, U=8, and N=1024. Assume that the CQIvalues are quantized in the step of 4-5 dB. The quantized CQI values aregiven by [−3, 1, 5, 10, 15, 20] dB with the following probability massfunction [0.05, 0.25, 0.25 0.20 0.15 0.10]. That is, 5% of the time,users will report CQI values lower than −3 dB, 25% of the time with CQIvalues between −3 and 1 dB, and so on. The access point can then adjustthe power for the acknowledgment channel based on the reported CQI.

Using the proposed access sequence partitioning technique, the resultingcollision probability is approximately 2.5%. The collision probabilityusing uniform access sequence partitioning compared is 3.3%. However, toget a similar collision probability when a uniform access sequencepartitioning is used, the total number of sequences has to be increasedby 25% to 1280. Accordingly, a larger number of access sequences tosearch translates directly to higher complexity and higher false alarmprobability.

This partitioning strategy can also be used when signaling otherinformation such as packet size, traffic type, and bandwidth requestover the access channel. This is particularly useful when the accesschannel (the preamble portion) is used as a means for users to get backinto the system or to request resources. If information regarding thestatistics of information to be conveyed is known (e.g., percentage oftimes a certain traffic connection (http, ftp, SMS) is requested or howmuch bandwidth is often required, etc.), then this information can beused in determining the partition of the access preamble sequence space.

FIG. 7 illustrates a table 700 stored in memory that partitions thegroup of access sequences into sub-groups of access sequences based on avariety of factors. Factors include CQI ranges, buffer level, quality ofservice, packet size, frequency bandwidth request, or other factors. Thequantity of access sequences in a given sub-group may be initiallydetermined on statistics maintained of past concentration of users inthe given cell as a function of the factors being considered. Thus, eachcell may have a predetermined mass distribution of access sequences forcombinations of the various factors. In so doing, the collisionprobability of multiple users selecting the same access sequence isminimized.

In an embodiment, the quantity of access sequences assigned to variouscombinations of factors may dynamically change based on changes in thecomposition of users needs. Thus, if a higher quantity of users migrateto a region with a CQI within a given range and a buffer level of acertain amount, and other various factors, that region may be assignedadditional access sequences. Dynamic allocation of access sequences thusmimics an optimal scenario whereby the collision probability isminimized.

FIG. 8 illustrates such a process 800. Initial partitions are set 804,thereby partitioning the plurality of access sequences into a number ofgroups of access sequences. These groups may be based on ranges of CQIvalues. In an embodiment, the initial set may be based on uniformdistribution of access sequences. In another embodiment, the initialpartition sizes may be based on historical data. A counter 808 countsthe access attempts in each subset. The counter can keep track of theaccess attempts over time to determine if there are patterns of varyingheavy or light usage. Based on this access attempts over time, theexpected value of access attempts in given subsets may be updated 812.The expected value may be represented by the following equation:

E _(m):=(1−β)E _(m) +βa _(m)(a _(m)−1)

where E_(m) is the expected value, a_(m) represents the quantity ofaccess sequences in a given subset, and β is the forgetting factor. Theforgetting factor computes an average recursively, that gives a largerweight to more recent data and a lesser weight to less recent data.

Based on the new expected value, the new subset size may be determined816. In an embodiment, the subset size is determined by the followingequation:

${N_{m} = {N\frac{\sqrt{E_{m}}}{\sum\limits_{k = 1}^{M}\; \sqrt{E_{k}}}}},{1 \leq m \leq M}$

where N_(m) is the new subset size, E_(k) is the “old” expectation valueof the k^(th) subset, m is the given subset out of M total subsets.

A determination is made 820 as to whether newly determined subset sizeis substantially different than the previously set subset size. Thethreshold for what constitutes “substantially different” isconfigurable. If a determination is made that the newly determinedsubset size is substantially different 824, then the subset sizes arereset. If not (828), the current subset sizes are maintained 832.

The various aspects and features of the present invention have beendescribed above with regard to specific embodiments. As used herein, theterms ‘comprises,’ ‘comprising,’ or any other variations thereof, areintended to be interpreted as non-exclusively including the elements orlimitations which follow those terms. Accordingly, a system, method, orother embodiment that comprises a set of elements is not limited to onlythose elements, and may include other elements not expressly listed orinherent to the claimed embodiment.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions and improvements fall withinthe scope of the invention as detailed within the following claims.

What is claimed is:
 1. A method of wireless communication, the methodcomprising: selecting an access sequence from a plurality of accesssequences; appending information to the access sequence, wherein theinformation comprises at least one of an indication of an amount of datato send, a priority group, a quality of service, or any combinationthereof; transmitting the access sequence and the information; receivingan access grant message defining at least one resource to be used; andsending data according to a defined at least one resource allocated inthe access grant.
 2. The method of claim 1, further comprising:determining an estimate of a channel quality based at least in part on ametric of an observed transmission; selecting a group of accesssequences from a plurality of groups of access sequences based at leastin part on comparing the determined estimate of channel quality to arange of channel quality values; and selecting an access sequence fromthe selected group of access sequences.
 3. The method of claim 1,wherein the access grant is sent to a group of access terminals.
 4. Themethod of claim 2, wherein the metric comprises a power of an observedpilot signal.
 5. The method of claim 2, wherein determining the estimateof channel quality further comprises determining a ratio of receivedpilot power to noise.
 6. The method of claim 2, wherein determining theestimate of channel quality further comprises determining a ratio ofreceived pilot power to a sum of received pilot and power and noise. 7.The method of claim 2, wherein a plurality of access sequences in theplurality of groups of access sequences are distributed non-uniformly.8. The method of claim 2, wherein transmitting further comprisestransmitting in accordance with a Frequency Division Multiplex (FDM)scheme.
 9. The method of claim 2, wherein transmitting further comprisestransmitting in accordance with a Code Division Multiplex (CDM) scheme.10. The method of claim 2, wherein transmitting further comprisestransmitting in accordance with an Orthogonal Frequency DivisionMultiple Access (OFDMA) scheme.
 11. An apparatus for wirelesscommunication, the apparatus comprising: means for selecting an accesssequence from a plurality of access sequences; means for appendinginformation to the access sequence, wherein the information comprises atleast one of an indication of an amount of data to send, a prioritygroup, a quality of service, or any combination thereof; means fortransmitting the access sequence and the information; means forreceiving an access grant message defining at least one resource to beused; and means for sending data according to a defined at least oneresource allocated in the access grant.
 12. The apparatus of claim 11,further comprising: means for determining an estimate of a channelquality based at least in part on a metric of an observed transmission;means for selecting a group of access sequences from a plurality ofgroups of access sequences based at least in part on comparing thedetermined estimate of channel quality to a range of channel qualityvalues; and means for selecting an access sequence from the selectedgroup of access sequences.
 13. The apparatus of claim 11, wherein theaccess grant is sent to a group of access terminals.
 14. The apparatusof claim 12, wherein the metric comprises a power of an observed pilotsignal.
 15. The apparatus of claim 12, wherein the means for determiningthe estimate of channel quality further comprises means for determininga ratio of received pilot power to noise.
 16. The apparatus of claim 12,wherein the means for determining the estimate of channel qualityfurther comprises means for determining a ratio of received pilot powerto a sum of received pilot and power and noise.
 17. The apparatus ofclaim 12, wherein a plurality of access sequences in the plurality ofgroups of access sequences are distributed non-uniformly.
 18. Theapparatus of claim 12, wherein the means for transmitting furthercomprises means for transmitting in accordance with a Frequency DivisionMultiplex (FDM) scheme.
 19. The apparatus of claim 12, wherein the meansfor transmitting further comprises means for transmitting in accordancewith a Code Division Multiplex (CDM) scheme.
 20. The apparatus of claim12, wherein the means for transmitting further comprises means fortransmitting in accordance with an Orthogonal Frequency DivisionMultiple Access (OFDMA) scheme.
 21. An apparatus for wirelesscommunication, the apparatus comprising: a selector configured to selectan access sequence from a plurality of access sequences; a processorconfigured to append information to the access sequence, wherein theinformation comprises at least one of an indication of an amount of datato send, a priority group, a quality of service, or any combinationthereof; a transmitter configured to transmit the access sequence andthe information; a receiver configured to receive an access grantmessage defining at least one resource to be used; and a transmitterconfigured to send data according to a defined at least one resourceallocated in the access grant.
 22. The apparatus of claim 21, theprocessor further configured to: determine an estimate of a channelquality based at least in part on a metric of an observed transmission;select a group of access sequences from a plurality of groups of accesssequences based at least in part on comparing the determined estimate ofchannel quality to a range of channel quality values; and select anaccess sequence from the selected group of access sequences.
 23. Theapparatus of claim 21, wherein the access grant is sent to a group ofaccess terminals.
 24. The apparatus of claim 22, wherein the metriccomprises a power of an observed pilot signal.
 25. The apparatus ofclaim 22, wherein the processor is further configured to determine aratio of received pilot power to noise.
 26. The method of claim 22,wherein the processor is further configured to determine a ratio ofreceived pilot power to a sum of received pilot and power and noise. 27.The apparatus of claim 22, wherein a plurality of access sequences inthe plurality of groups of access sequences are distributednon-uniformly.
 28. The apparatus of claim 22, wherein the processor isfurther configured to transmit in accordance with a Frequency DivisionMultiplex (FDM) scheme.
 29. The apparatus of 22, wherein the processoris further configured to transmit in accordance with a Code DivisionMultiplex (CDM) scheme.
 30. The apparatus of claim 22, wherein theprocessor is further configured to transmit in accordance with anOrthogonal Frequency Division Multiple Access (OFDMA) scheme.